Qiagen DNAeasy blood&tissue DNA isolation kit

Is there anyone use Qiagen DNAeasy blood&tissue DNA isolation kit? I was useing this kit to isolate DNA from the tail of mice for genotyping. I had a lot of problem with the genotyping PCR these days. I changed the PCR reagents, but still don't work. Then I measured the DNA concentration and found that the concentration is as low as 20ng per microlitle.
I am asking if anyone here had the same bad experience and any of your suggestion will be appreciated.
thanks